Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Adjusting Backlash on Skywatcher AZ-Gti Mount

  • Please log in to reply
13 replies to this topic

#1 moxican

moxican

    Viking 1

  • -----
  • topic starter
  • Posts: 643
  • Joined: 13 Nov 2011
  • Loc: Toronto, Canada

Posted 16 July 2019 - 12:05 AM

I have been using the Skywatcher AZ-Gti for about a month now, and although initially it was pretty good, it has developed a significant amount of backlash on its declination axis. This is a well documented subject on CN. So, against all odds and other people suggestions on CN to just leave with it, I had to find a way to make it at least more acceptable. That is just the way I am built.

Thus, I am making this tutorial on how I did it. It will require patience and I'd say intermediate tinkering skills. Make sure you understand that you do this at your own risk!!! You break something the mount is finished. I'd say the entire endeavor took me somewhere between 2-3 hours, but I am quite handy.

 

Tools you will need:

- a mid to large size flat screwdriver

- a small flat screwdriver

- 1.5 mm (metric) Allen key (hex key)

- a small Philips screwdriver, it needs to be able to reach into small holes to about 1/2 - 3/4 inch

- optional - some machinery grease

- favorite drink

 

The very first thing you want to do is to disconnect your mount from any power source. If you use a 12V battery make sure it is unplugged from the mount, if you use batteries remove them all!

Second thing, untwist the declination knob all the way until it comes separate from the mount. From here on you will void the warranty of your SW mount.

There are six fairly small screws that hold the black plastic cover onto the white metal housing. You need to remove this plastic cover in order to gain access to the inside of the mechanics so go ahead and remove them. I have marked them on the following images.

 

Screws-1.jpg

 

Screws-2.jpg

 

Now, carefully remove the plastic, there are wires running to it. You don't want to break any of these cables!!! On the inside you will see two large gears, one for the declination and one for the right ascension axis on each side of the mount along with their motor drive unit. After some investigation and trial and error, I found out that contrary to the belief out there the issue is not located between the declination gear and its driving gear. Its location is in the motor unit's gearbox. See attached image...

 

Backlash-location.jpg

 

To illustrate the amount of backlash that was in the gearbox, click on this link. It is a considerable amount and something PHD2 was unable to cope with... understandably.


Edited by moxican, 16 July 2019 - 12:51 AM.

  • Live_Steam_Mad, Cometeer, RazvanUnderStars and 5 others like this

#2 moxican

moxican

    Viking 1

  • -----
  • topic starter
  • Posts: 643
  • Joined: 13 Nov 2011
  • Loc: Toronto, Canada

Posted 16 July 2019 - 12:32 AM

In order to successfully fix this issue, the entire motor control unit has to be removed. I have marked the bolt and screws that needs to be dealt with.

 

Mount-inside.jpg

 

Screw# 1 is optional to take out. It is responsible for having spring loading the control box to the declination gear. The spring hook can simply be unhooked and re-hooked. It is a bit of a pain in the a** to put it back.

Screw#2 is really a bolt and a screw. Make sure you loosen the bolt first! The screw inside the bolt is very brittle and if you break off the top slit, you will have no way of working with it. I am not sure what size is the bolt, it is not really tight, I used a small pliers to remove it. When this is done, you want to make sure you remove that inside screw as well, that the bolt was hanging onto. You keep unscrewing and it will come loose eventually.

Screw# 3 is just a screw to fix the other end of the unit to the declination gear. In fact perhaps it's best to remove this screw before you remove screw# 2. Your choice on this one.

 

The entire motor drive unit is loose but don't just yank it out yet. You have to disconnect it's power cable first. It is just a simple but careful pull.

 

 

 

Now you have the unit to work with. In order to make the necessary adjust to the gearbox, you need to remove the main gear that is fixed to the end of the motor axle. Both gears will have two small hex screws to hold them tight to their axes. I have made two yellow marks. I circled the hex screw which needs to be found on the gear the arrow points to. The arrow also points to the service openings to have access to these hex screws. You will need a 1.5 mm Allen key for this move. If the screw do not line up with the service holes you can turn them by rotating the small plastic gear on the other end of the entire unit. You don't have to remove the gear on the drive axle for the large declination gear.

 

 

 

 

Attached Thumbnails

  • Cable-to-disconnect.jpg

  • RazvanUnderStars and Michal Juul like this

#3 moxican

moxican

    Viking 1

  • -----
  • topic starter
  • Posts: 643
  • Joined: 13 Nov 2011
  • Loc: Toronto, Canada

Posted 16 July 2019 - 12:48 AM

After removing the small gear, you will see three small screws right under it. These screws are the one that hold the metal housing of the drive unit together.

 

Adjusting-gear-housing.jpg

 

You need to loosen all three screws (no need to take them out completely), and push the frame downward shown as an arrow on the picture. This will ensure that the two gears will lock together tight and won't have that play that I have shown on the first post. Once you have done adjusting the frame, hold it there until you fasten all three screws back again. From here on you just simply track your steps backward, and re-assemble everything. Just look at how tight the gears are after I put the gear back on mine!

 

Tight-gears-finish.jpg

 

This last step is more of a suggestion. I decided to put some automotive grease on the gears. Hear in Canada we get some pretty cold winters and the factory grease Skywatcher put on becomes sticky and rigid in those frigid temperatures. 

 

Optional-greasing.jpg

 

I did not remove the gear box for the RA axis as the backlash there is minimal, but if that is something you need to tune up as well, same steps apply

 

Unfortunately I did not have a chance to test it under a star studded night. Clouds are so dark here tonight I don't know if the Sun will be able to penetrate tomorrow morning, but that is how usually go when you want to test equipment around here smirk.gif . But I did try it out indoors with camera and slowest slewing speed, and it looks very promising. Backlash is noticeably less then it was before the tune up. I want to put PHD2 on it and test the hell out of it to see how it performs.


Edited by moxican, 16 July 2019 - 12:57 AM.

  • Live_Steam_Mad, S.Boerner, RazvanUnderStars and 2 others like this

#4 tkottary

tkottary

    Mariner 2

  • -----
  • Posts: 268
  • Joined: 06 Dec 2015
  • Loc: San Jose,CA

Posted 16 July 2019 - 12:59 AM

Thank you for this! 



#5 Michal Juul

Michal Juul

    Lift Off

  • -----
  • Posts: 21
  • Joined: 16 Feb 2018
  • Loc: Denmark

Posted 16 July 2019 - 02:00 AM

It's a really good tutorial. Thank you so much waytogo.gif



#6 DIMITRIS K.

DIMITRIS K.

    Vostok 1

  • -----
  • Posts: 109
  • Joined: 23 Aug 2017
  • Loc: Athens, Greece

Posted 16 July 2019 - 07:11 AM

Wow! My congrats for your tutorial. I'll try this to my mount to see if i have any more improvement! 



#7 trurl

trurl

    Voyager 1

  • *****
  • Posts: 14604
  • Joined: 10 Jul 2017
  • Loc: North Carolina

Posted 16 July 2019 - 07:35 AM

bow.gif waytogo.gif like-button.jpg



#8 moxican

moxican

    Viking 1

  • -----
  • topic starter
  • Posts: 643
  • Joined: 13 Nov 2011
  • Loc: Toronto, Canada

Posted 16 July 2019 - 09:12 AM

No problem gentlemen. Make sure that before you put the final plastic cover back on the mount you test the gears and make a full rotation of the adjusted axis, in my case the declination. Do it at highest speed and listen to the mechanics. If you hear at any point that the motor is exerting more power to keep turning or it is getting out of "breath", you have to loosen the tension adjustment. You gears are binding up there. 


  • davidparks likes this

#9 Biggen

Biggen

    Vostok 1

  • *****
  • Posts: 153
  • Joined: 04 Jan 2019

Posted 17 July 2019 - 06:48 PM

This is great. I’m going to try this I think this weekend.

 

Great job. Be sure to report back when you try guiding with PHD2 again.



#10 Bowlerhat

Bowlerhat

    Mariner 2

  • -----
  • Posts: 258
  • Joined: 05 Jun 2019
  • Loc: Melbourne, Australia

Posted 17 July 2019 - 07:02 PM

Thank you, this is helpful. Last time I used it I got backlash as well, might need to open it up.



#11 DIMITRIS K.

DIMITRIS K.

    Vostok 1

  • -----
  • Posts: 109
  • Joined: 23 Aug 2017
  • Loc: Athens, Greece

Posted 18 July 2019 - 11:53 PM

Yesterday i was trying to fine adjust my mount. My problem is that when i'm trying to correct a backlash in the first half of the mount as it rotates, i get a gear tension in the other half and i head the motor struggle and vice versa. This is minimal without load, but it's obvious with all my gear loaded on the mount. The best i manage to do is to find a balance between those two. I have a little backlash on the first half and little tension on the other half. But as mutch as i try, i can't find a "sweet spot" to eliminate both. Do you experience the same problem?



#12 moxican

moxican

    Viking 1

  • -----
  • topic starter
  • Posts: 643
  • Joined: 13 Nov 2011
  • Loc: Toronto, Canada

Posted 19 July 2019 - 08:08 AM

I did not see any tension on mine. One thing you need to know though, the quality on this mount varies wildly. Some people report absolutely no backlash, other people report so much of it that they can barely use it for visual observation. 

I have adjusted mine and although it has gotten better it is still too large for PHD2 to deal with. Those of us who tried to contact Skywatcher got the "it is supposed to be like that" reply and a disclaimer that they have never design this for astrophotography.


  • DIMITRIS K. and Bowlerhat like this

#13 DIMITRIS K.

DIMITRIS K.

    Vostok 1

  • -----
  • Posts: 109
  • Joined: 23 Aug 2017
  • Loc: Athens, Greece

Posted 19 July 2019 - 03:09 PM

My first mount had a lot of issues. Tracking was so bad that i didn't manage to get a picture from Sharpcap without star trails. I' ve managed to get an acceptable tracking from time to time but then i had a lot of wi fi disconnections. And go to was too far away from target all the time. I've returned it to my vendor and had a replacement with a brand new, that  i use  now. This mount is way better from the first one, but sometimes i struggle again with tracking issues. I must play with the arrow keys to make it track right, but i' ve managed to do a 5 minute stacking without significant problems. It seems to need a "push" for the gears to engage right. Skywatcher must reconsider it's quality control with that one. But i suspect it had desing flaws that must improve with a second revision. Too bad that i can't use it for imaging, because it's small and super easy to setup for some quick low exposures and i must rely on my perfect but time consuming to setup and run SXD2 for that. Maybe i asked too much for this price tag, but if it's working right from time to time, why not working right all the time? 


Edited by DIMITRIS K., 19 July 2019 - 04:21 PM.

  • Live_Steam_Mad likes this

#14 moxican

moxican

    Viking 1

  • -----
  • topic starter
  • Posts: 643
  • Joined: 13 Nov 2011
  • Loc: Toronto, Canada

Posted 19 July 2019 - 05:08 PM

My first mount had a lot of issues. Tracking was so bad that i didn't manage to get a picture from Sharpcap without star trails. I' ve managed to get an acceptable tracking from time to time but then i had a lot of wi fi disconnections. And go to was too far away from target all the time. I've returned it to my vendor and had a replacement with a brand new, that  i use  now. This mount is way better from the first one, but sometimes i struggle again with tracking issues. I must play with the arrow keys to make it track right, but i' ve managed to do a 5 minute stacking without significant problems. It seems to need a "push" for the gears to engage right. Skywatcher must reconsider it's quality control with that one. But i suspect it had desing flaws that must improve with a second revision. Too bad that i can't use it for imaging, because it's small and super easy to setup for some quick low exposures and i must rely on my perfect but time consuming to setup and run SXD2 for that. Maybe i asked too much for this price tag, but if it's working right from time to time, why not working right all the time? 

Well, based on what you just said here, which I've heard from other users as well, it is unfit for visual use as well. Quality control would be the culprit, but that is too much of an expectation from Skywacther, it's a Chinese company, they just won't care.

And lastly, no... you are not expecting too much from that price tag. You'd be if it cost $100.


  • DIMITRIS K. likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics